Method for manufacturing polarizing plate polarizing plate optical film and image viewing display

ABSTRACT

A method for manufacturing a polarizing plate in which a transparent protective film is provided on at least one surface of a polarizer with an adhesive layer interposed therebetween, wherein an adhesive is coated on a surface of the transparent protective film on which the adhesive layer is formed or/and a surface of the polarizer on which the adhesive layer is formed to form the adhesive layers, and thereafter, an aqueous liquid is caused to be present on an adhering surface when the transparent protective film and the polarizer are continuously adhered to each other with the adhesive layer interposed therebetween. A polarizing plate having uniform polarization characteristics, and excellent in durability is obtained by the method.

TECHNICAL FIELD

The invention relates to a method for manufacturing a polarizing plate.The invention further relates to a polarizing plate obtained by themanufacturing method. The polarizing plate, alone as it is or as anoptical film manufactured by laminating the polarizing plates, can forma liquid crystal display (hereinafter referred to as LCD for short), aflat panel display such as an electroluminescence display (hereinafterreferred to as ELD for short) or an image viewing display such as PDP.

BACKGROUND ART

A polarizing plate for a flat panel display, especially a polarizingplate used in LCD, generally employs a polyvinyl alcohol (PVA)-basedfilm with a thickness of 70 μm or more mainly as a raw material. Inorder to obtain sufficient optical characteristics as LCD, preferablyused is a polarizing plate manufactured by stretching a PVA-based filmcontaining a dichroic material such as iodine and adhering a transparentprotective film onto the stretched PVA based film. The polyvinylalcohol-based polarizer is stretched in its manufacture; therefore thepolarizer is easy to shrink. Since a PVA-based film is made of ahydrophilic polymer, the film is very easily deformed especially in ahumidified condition. Moreover, since a mechanical strength of the filmitself is low, the film has a problem of tearing. Hence, transparentprotective films such as a film made of saponified triacetyl celluloseare adhered onto both sides or one side of a polarizer to therebysupplement its mechanical strength for its actual use. The polarizingplate is manufactured by adhering a transparent protective film to apolarizer with an adhesive. An aqueous adhesive is preferably used as anadhesive for a polarizing plate used in adhering a transparentprotective film to a polarizer: an example thereof is a polyvinylalcohol-based adhesive obtained by mixing a crosslinking agent into apolyvinyl alcohol aqueous solution.

Improvement on uniformity and quality of a screen image has beendemanded in company with progress in high definition and highfunctionality of LCD. A heat resistance, a wet heat resistance and awater resistance at high levels have been requested because of a trendto more of diversification in usage environment. A low profile andweight reduction of LCD have also been required because of a trend to afunction of portability in recent years. Requirements directed to apolarizing plate for LCD, from such required characteristics of LCD,include: higher performance and higher functionality as a polarizer atvarious angles such as uniformity, high heat resistance, high wet heatresistance, water resistance, low profile and the like.

A method for manufacturing a polarizing plate by adhering a transparentprotective film onto a polarizer is exemplified as follows: First ofall, as one method, an adhesive solution is coated on one surface of thepolarizer and thereafter, a transparent protective film is adhered tothe one surface. Then, the adhesive solution is coated onto the othersurface of the polarizer and thereafter, a transparent protective filmis adhered to the other surface thereof. Thereby, the transparentprotective films are adhered to both surfaces of the polarizer with theadhesive layers interposed therebetween to thereby manufacture apolarizing plate. Note that the adhesive solution is coated directly onthe transparent protective film or the adhesive solution is coated onboth of the polarizer and the transparent protective film. Anothermethod has been proposed in which, transparent protective films aredisposed on both surfaces of a polarizer and the transparent protectivefilms and the polarizer are caused to continuously pass through betweenrolls in a pair while an adhesive solution is supplied to therebetween(see JP-A No. 11-179871), or alternatively, transparent protective filmsand a polarizer are caused to continuously pass through between rolls ina pair in a state where adhesive layers are formed by coating anadhesive on surfaces of the transparent protective films on each ofwhich adhesive layers are formed or/and an adhesive layer is formed bycoating an adhesive on a surface of a polarizer on which the adhesivelayer is formed, and the transparent protective films are adhered to thepolarizer by a pressure of the rolls, thereby manufacturing a polarizingplate.

In the conventional process, however, a problem has been arisen thatstripe-shaped appearance faults are generated during adhesion of thetransparent protective films and the polarizer. Such a stripe-shapedappearance faults exerts an adverse influence on required highcharacteristics of a polarizing plate, especially on an opticaluniformity among them. Therefore, there has been a reality that aprogress in the related technology cannot cope with improvement onuniformity and quality of a screen image required in company withprogress toward higher definition and higher functionality of LCD. Theterm “stripe-shaped appearance faults” means a view of in the absorptionaxis direction of a polarizing plate obtained by adhering a transparentprotective film thereto, when being visually observed, as a reflectionimage of stripes parallel to one another. A feature of the stripes is tobe recognized as track grooves cut on a phonograph record with a pitchin the range of 1 to 2 mm.

A polarizer is used as a polarizing plate reinforced by a transparentprotective film in strength. A case has been conventionally arisen,however, where a polyvinyl alcohol-based adhesive causes separation atthe interface between the polarizer and the transparent protective filmin a humidified condition. A possibility can be assumed as a causethereof that a polyvinyl alcohol-based resin, which is a main componentof the adhesive, is a water-soluble polymer, suffers dissolution thereofinto water of dew condensates.

In order to solve such a problem, a resin solution including a polyvinylalcohol-based resin having an acetoacetyl group therein and acrosslinking agent is employed as a PVA-based adhesive to therebyimprove wet heat resistance and water resistance (see JP-A No.7-198945). However, a wafer resistance of an adhesive for a polarizingplate, which is described in an embodiment in JP-A No. 7-198945., hasbeen insufficient. Moreover, the adhesive has been insufficient becauseof stripe-shaped appearance faults.

A method has been proposed in which an adhesive layer is provided on apolarizer or a transparent protective film and a contact angle of theadhesive layer is previously controlled at a predetermined angle or lessby humidification and thereafter, the polarizer and the transparentprotective film is adhered to each other to thereby manufacture apolarizing plate (see JP-A Nos. 7-306315 and 7-306316). In the methodsof JP-A Nos. 7-306315 and 7-306316, a control is difficult and afabrication process is complicated; therefore, the methods cannot besaid to be practical manufacturing methods.

DISCLOSURE OF INVENTION

The invention has been made in light of such circumstances and it is anobject of the invention to provide a method for efficientlymanufacturing a polarizing plate having uniform polarizationcharacteristics, and excellent in durability.

It is a further object of the invention to provide a polarizing plateobtained by the manufacturing method. It is a still further object ofthe invention to provide an optical film obtained by laminating thepolarizing plates and an image viewing display such as LCD and ELD usingthe polarizing plate and the optical film.

The inventors have conducted serious studies in order to solve the abovetasks with findings that the objects can be achieved with an adhesivefor polarizing plate shown below, having led to completion of theinvention.

1. A method for manufacturing a polarizing plate in which a transparentprotective film is provided on at least one surface of a polarizer withan adhesive layer interposed therebetween, wherein

an adhesive is coated on a surface of the transparent protective film onwhich the adhesive layer is formed or/and a surface of the polarizer onwhich the adhesive layer is formed to form the adhesive layers, andthereafter,

an aqueous liquid is caused to be present on an adhering surface whenthe transparent protective film and the polarizer are continuouslyadhered to each other with the adhesive layer interposed therebetween.

2. The method for manufacturing the polarizing plate above-mentioned 1,wherein the polarizer is a polyvinyl alcohol-based polarizer and thetransparent protective film is a cellulose-based transparent protectivefilm.

3. The method for manufacturing the polarizing plate above-mentioned 1or 2, wherein a thickness of the polarizer is 35 μm or less.

4. The method for manufacturing the polarizing plate above-mentioned anyone of 1 to 3, wherein the adhesive is a polyvinyl alcohol-basedadhesive.

5. The method for manufacturing the polarizing plate above-mentioned 4,wherein the polyvinyl alcohol-based adhesive is a polyvinylalcohol-based adhesive having an acetoacetyl group.

6. The method for manufacturing the polarizing plate above-mentioned anyone of 1 to 5, wherein the adhesive comprises a crosslinking agent.

7. The method for manufacturing the polarizing plate above-mentioned 6,wherein the crosslinking agent is a methylol compound.

8. The method for manufacturing the polarizing plate above-mentioned anyone of 1 to 7, wherein a thickness of the adhesive layer is in the rangeof 30 to 300 nm.

9. The method for manufacturing the polarizing plate above-mentioned anyone of 1 to 8, wherein a viscosity of the aqueous liquid is in the rangeof 0.1 to 10 cP.

10. The method for manufacturing the polarizing plate above-mentionedany one of 6 to 9, wherein the aqueous liquid is water.

11. The method for manufacturing the polarizing plate above-mentionedany one of 1 to 9, wherein the aqueous liquid is an aqueous solutioncomprising a crosslinking agent dissolved therein.

12. The method for manufacturing the polarizing plate above-mentioned11, wherein the crosslinking agent is a methylol compound.

13. The method for manufacturing the polarizing plate above-mentionedany one of 1 to 12, wherein the aqueous liquid is supplied on anadhering surface between the transparent protective film and thepolarizer.

14. The method for manufacturing the polarizing plate above-mentionedany one of 1 to 12, wherein the adhesive is coated only onto thetransparent protective film side and the aqueous liquid is supplied onthe adhesive layer formed by the coating to thereby cause the aqueousliquid to be present on the adhering surface.

15. The method for manufacturing the polarizing plate above-mentionedany one of 1 to 12, wherein the adhesive is coated only onto thetransparent protective film side, while the aqueous liquid is suppliedonto the polarizer side to thereby cause the aqueous liquid to bepresent on the adhering surface.

16. The method for manufacturing the polarizing plate above-mentionedany one of 1 to 12, wherein the adhesive is coated only onto thepolarizer side, while the aqueous liquid is supplied onto thetransparent protective film side to thereby cause the aqueous liquid tobe present on the adhering surface.

17. The method for manufacturing the polarizing plate above-mentionedany one of 1 to 16, wherein the aqueous liquid is supplied onto anadhering surface just before adhesion when the transparent protectivefilm and the polarizer are continuously adhered to each other with theadhesive layer interposed therebetween.

18. A polarizing plate obtained by the method above-mentioned any one of1 to 17.

19. An optical film comprising at least one polarizing plateabove-mentioned 18.

20. An image viewing display comprising the polarizing plateabove-mentioned 18 or the optical film above-mentioned 19.

In the methods for manufacturing the polarizing plate of the invention,an adhesive is coated on a surface of at least one of a transparentprotective film and a polarizer to thereby manufacture the transparentprotective film or the polarizer on which an adhesive layer has beenformed thereon before the polarizer and the transparent protective filmare adhered to each other with an adhesive agent. Then, in adhesion ofthe transparent protective film to the polarizer, an aqueous liquid iscaused to be present on an adhering surface, that is, the adhesivelayer, of the transparent protective film and the polarizer. Hence, apolarizing plate is obtained that has suppressed generation ofappearance faults, especially stripe-shaped irregularity. Such apolarizing plate is suppressed with respect to stripe-shaped appearancefaults, which make it possible to provide an image viewing display suchas a high performance LCD and a high performance ELD with uniformpolarization characteristics. The manufacturing method of the inventionis suited for a continuous manufacture to thereby enable a polarizingplate to be manufactured with good efficiency. Addition of an aqueousliquid to an adhesive layer enables a polarizing plate to be excellentin durability. Especially in a case where an adhesive is a polyvinylalcohol-based adhesive having an acetoacetyl group and contains amethylol melamine as a crosslinking agent, durability of the adhesive isimproved.

A detailed mechanism is not clear of the fact that a manufacturingmethod of the invention is effective for suppression of stripe-shapedappearance faults occurring in a polarizing plate. The reason forgenerating stripe-shaped appearance faults in a conventionalmanufacturing method as described above is guessed that an adhesivesolution with a high viscosity is brought into contact with a surface ofa polarizer or a transparent protective film in the course of adhesionof the transparent protective film to the polarizer, which, as aphysical factor, exerts a physical force on the polarizer, while in theinvention, the physical factor seems to be eliminated due to thepresence of an aqueous liquid.

It has also found, as a surprise, that in a manufacturing method of theinvention, an adhesive with a higher reactivity is more effective insuppression of generation of such stripe-shaped appearance faults thanan adhesive with a lower reactivity. A mechanism thereof is notnecessarily cleared. Since an adhesive with a low reactivity isgenerally higher in dissolubility in water, an adhesive layer onceformed on a surface of a transparent protective film or a polarizer isredissolved into an added aqueous liquid. The reason for suppressinggeneration of such stripe-shaped faults is imagined that a viscosity ofthe added aqueous solution is increased by the redissolution in thevicinity of a surface of the polarizer or the transparent protectivefilm as a counterpart to be adhered. Therefore, a manufacturing methodof the invention is especially effective for an adhesive with a highreactivity.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an example of a schematic view of a method for manufacturing apolarizing plate of the invention.

FIG. 2 is an example of a schematic view of a method for manufacturing apolarizing plate of the invention.

FIG. 3 is an example of a schematic view of a conventional method formanufacturing a polarizing plate.

FIG. 4 is an example of a schematic view of a conventional method formanufacturing a polarizing plate.

BEST MODE FOR CARRYING OUT THE INVENTION

Various kinds of polarizers can be used without imposing a specificlimitation on thereon. Examples of the polarizers include: hydrophilicpolymer films, such as a polyvinyl alcohol-based film, a partiallyformalized polyvinyl alcohol-based film and an ethylene vinyl acetatecopolymer-based partially saponified film, obtained by adsorbing adichroic material such as iodine or a dichroic dye on the films and thenuniaxially stretching them; orientation films of polyenes such as adehydrated polyvinyl alcohol and dehydrochlorinated polyvinyl chloride.Among them, preferable is a polarizer comprising a polyvinylalcohol-based film and a dichroic material such as iodine or a dichroicdye.

A polyvinyl alcohol-based film that can be properly used is formed as afilm by means of any one of methods such as a flow casting method, inwhich an undiluted liquid prepared by dissolving a polyvinylalcohol-based resin into water or an organic solvent is caused toflow-cast on a surface to form a film, a casting method or an extrusionmethod. A polymerization degree of a polyvinyl alcohol-based resin ispreferably in the range of about 100 to 5000 and more preferably in therange of 1400 to 4000.

A polarizer obtained by dyeing a polyvinyl alcohol-based film withiodine or the like and stretching the dyed film uniaxially ismanufactured, for example, according to the following method.

In a dyeing step, a polyvinyl alcohol-based film is immersed in a dyebath into which iodine is added at a temperature in the range of about20 to 70° C. for a time ranging 1 to 20 min to thereby cause iodine tobe adsorbed thereon. An iodine concentration of the dye bath is usuallyin the range of about 0.1 to 1 part by weight relative to 100 parts byweight of water. An assistant such as iodides may be added into the dyebath in the range of about 0.02 to 20 parts by weight and preferably inthe range of 2 to 10 parts by weight, examples of the iodides including:potassium iodide, lithium iodide, sodium iodide, zinc iodide, aluminumiodide, lead iodide, copper iodide, barium iodide, calcium iodide, tiniodide, titanium iodide and the like. An iodide described above isespecially preferable in order to increase a dyeing efficiency. A smallamount of an organic solvent compatible with water may be incorporatedtherein in addition to water solvent.

A polyvinyl alcohol-based film may also be subjected to a swellingtreatment in a water bath or the like at a temperature in the range ofabout 20 to 60° C. for a time in the range of about 0.1 to 10 min beforedyeing in an aqueous solution containing iodine or a dichroic dye. Inthe swelling treatment in the water bath, not only is the polyvinylalcohol-based film water washed to thereby enable contamination and ablocking preventive agent on a surface of the polyvinyl alcohol-basedfilm to be cleaned but an effect of swelling the polyvinyl alcohol-basedfilm is also exerted to thereby prevent ununiformity such as dyeingirregularity.

The dyeing treated polyvinyl alcohol-based film can be crosslinked whenrequired. A composition of a crosslinking aqueous solution forcrosslinkage is such that a crosslinking agent such as boric acid,borax, glyoxal or glutaraldehyde alone or in mixture is usuallycontained in the range of about 1 to 10 parts by weight relative to 100parts by weight of water. A concentration of a crosslinking agent isdetermined in consideration of a balance between an opticalcharacteristics and shrinkage of a polarizing plate caused by astretching force generated in the polyvinyl alcohol-based film.

An assistant such as iodides may be added into a crosslinking bath inthe range of 0.05 to 15 wt % and preferably in the range of 0.5 to 8 wt%; examples of the iodides including: potassium iodide, lithium iodide,sodium iodide, zinc iodide, aluminum iodide, lead iodide, copper iodide,barium iodide, calcium iodide, tin iodide, titanium iodide and the like.An additive described above is especially preferable because of in-planeuniform characteristics of a polarizer. A temperature of an aqueoussolution is usually in the range of about 20 to 70° C. and preferably inthe range of 40 to 60° C. An immersion time is not specifically limited,but usually in the range of about 1 sec to 15 min and preferably in therange of 5 sec to 10 min. A small amount of an organic solventcompatible with water may be contained in addition to an aqueoussolvent.

A total stretch magnification of a polyvinyl alcohol-based film is inthe range of about 3 to 7 times and preferably in the range of 5 to 7 aslong as the original length. If a total stretch magnification exceeds 7times, the film is easy to be broken. Stretching may be conducted eitherafter dyeing, while dyeing or crosslinking, or stretching may befollowed by dyeing with iodine. The stretch method, the number of timesof stretches or the like is not specifically limited and a stretch maybe conducted only in one step. Alternatively, plural times of stretchesmay be conducted in the same step.

A polyvinyl alcohol-based film having been subjected to aniodine-adsorption orientation treatment can be subjected to a step offurther immersing the film in an potassium iodide of aqueous solutionwith a concentration of 0.1 to 10 mass % at a temperature in the rangeof about 10 to 60° C. and preferably in the range of about 30 to 40° C.for a time in the range of 1 sec to 1 min. An assistant such as zincsulfate or zinc chloride may be added into an aqueous iodine solution. Apolyvinyl alcohol-based film having been subjected to theiodine-adsorption orientation treatment may be treated with awater-washing step and a drying step at a temperature in the range ofabout 20 to 80° C. for a time in the range of about 1 min to 10 min.

No specific limitation is imposed on a thickness of a polarizer, butgenerally is in the range of about 5 to 80 μm. If a thickness thereof isthinner, water in a polarizer is easier to be evaporated in a dryingstep or the like in adhesion of a transparent protective film to thepolarizer in a manufacturing process of the polarizing plate. Hence, anelongation of the polarizer decreases to thereby easily generateconspicuous stripe-shaped appearance faults. Such a phenomenon is moreconspicuously observed as a thickness of the polarizer is smaller, butaccording to a manufacturing method for a polarizing plate of theinvention, generation of stripe-shaped appearance faults can besuppressed in a case where a thickness of the polarizer is 35 μm or lessand furthermore even in a case where a thickness of the polarizer is 20μm or less.

Proper transparent materials may be used as a transparent polymer or afilm material that forms the transparent protective file, and thematerial having outstanding transparency, mechanical strength, heatstability and outstanding moisture interception property, etc. may bepreferably used. As materials of the above-mentioned transparentprotective film, for example, polyester type polymers, such aspolyethylene terephthalate and polyethylenenaphthalate; cellulose typepolymers, such as diacetyl cellulose and triacetyl cellulose; acrylicstype polymer, such as poly methylmethacrylate; styrene type polymers,such as polystyrene and acrylonitrile-styrene copolymer (AS resin);polycarbonate type polymer may be mentioned. Besides, as examples of thepolymer forming a transparent protective film, polyolefin type polymers,such as polyethylene, polypropylene, polyolefin that has cyclo- type ornorbornene structure, ethylene-propylene copolymer; vinyl chloride typepolymer; amide type polymers, such as nylon and aromatic polyamide;imide type polymers; sulfone type polymers; polyether sulfone typepolymers; polyether-ether ketone type polymers; poly phenylene sulfidetype polymers; vinyl alcohol type polymer; vinylidene chloride typepolymers; vinyl butyral type polymers; arlylate type polymers;polyoxymethylene type polymers; epoxy type polymers; or blend polymersof the above-mentioned polymers may be mentioned. The transparentprotective film is formed as a cured layer made of heat curing type orultraviolet ray curing type resins, such as acryl based, urethane based,acryl urethane based, epoxy based, and silicone based, etc.

Moreover, as is described in Japanese Patent Laid-Open Publication No.2001-343529 (WO 01/37007), polymer films, for example, resincompositions including (A) thermoplastic resins having substitutedand/or non-substituted imido group in sidechain, and (B) thermoplasticresins having substituted and/or non-substituted phenyl and nitrilegroup in sidechain may be mentioned. As an illustrative example, a filmmay be mentioned that is made of a resin composition includingalternating copolymer comprising iso-butylene and N-methyl maleimide,and acrylonitrile-styrene copolymer. A film comprising mixture extrudedarticle of resin compositions etc. may be used. Since the films are lessin retardation and less in photoelastic coefficient, faults such asunevenness due to a strain in a polarizing plate can be removed andbesides, since they are less in moisture permeability, they areexcellent in durability under humidified environment.

A thickness of the transparent protective film can be properlydetermined and generally on the order in the range of from about 1 toabout 500 μm from the viewpoint of a strength, workability such ashandlability, requirement for a thin film and the like. Especially, thethickness is preferably in the range of from 1 to 300 μm and morepreferably in the range of from 5 to 200 μm. The transparent protectivefilm having a thickness of 50 μm or less is preferably used.

Moreover, it is preferable that the transparent protective film may haveas little coloring as possible. Accordingly, a transparent protectivefilm having a retardation value in a film thickness directionrepresented by Rth=[(nx+ny)/2−nz]×d of from −90 nm to +75 nm (where, nxand ny represent principal indices of refraction in a film plane, nzrepresents refractive index in a film thickness direction, and drepresents a film thickness) may be preferably used. Thus, coloring(optical coloring) of polarizing plate resulting from a transparentprotective film may mostly be cancelled using a transparent protectivefilm having a retardation value (Rth) of from −90 nm to +75 nm in athickness direction. The retardation value (Rth) in a thicknessdirection is preferably from −80 nm to +60 nm, and especially preferablyfrom −70 nm to +45 nm.

As transparent protective films, preferable are a cellulose-basedpolymer such as triacetyl cellulose from the standpoint of apolarization characteristic, a durability or the like. Especiallypreferable is a triacetyl cellulose film. Note that in a case wheretransparent protective films are provided on both sides of a polarizer,the transparent protective films made from the same polymer may be usedon both sides thereof or alternatively, the transparent protective filmsmade from polymer materials different from each other may also be usedon respective both sides thereof.

An easy adhesion treatment can be applied onto a surface of atransparent protective film which is adhered to a polarizer. Examples ofeasy adhesion treatments include: dry treatments such as a plasmatreatment and a corona treatment; chemical treatment such as alkalinetreatment; and a coating treatment in which an easy adhesion layer isformed. Among them, preferable are a coating treatment and an alkalinetreatment each forming an easy adhesion layer. In formation of an easyadhesion layer, there can be used each of various kinds of easy adhesionmaterials such as a polyol resin, a polycarboxylic resin and a polyesterresin. Note that a thickness of an easy adhesion layer is preferablyusually from about 0.01 to about 10 μm, more preferably from about 0.05to about 5 μm and especially preferably from about 0.1 to 1 μm.

A hard coat layer may be prepared, or antireflection processing,processing aiming at sticking prevention, diffusion or anti glare may beperformed onto the face on which the polarizing film of the abovedescribed transparent protective film has not been adhered.

A hard coat processing is applied for the purpose of protecting thesurface of the polarizing plate from damage, and this hard coat film maybe formed by a method in which, for example, a curable coated film withexcellent hardness, slide property etc. is added on the surface of thetransparent protective film using suitable ultraviolet curable typeresins, such as acrylic type and silicone type resins. Antireflectionprocessing is applied for the purpose of antireflection of outdoordaylight on the surface of a polarizing plate and it may be prepared byforming an antireflection film according to the conventional method etc.Besides, a sticking prevention processing is applied for the purpose ofadherence prevention with adjoining layer.

In addition, an anti glare processing is applied in order to prevent adisadvantage that outdoor daylight reflects on the surface of apolarizing plate to disturb visual recognition of transmitting lightthrough the polarizing plate, and the processing may be applied, forexample, by giving a fine concavo-convex structure to a surface of thetransparent protective film using, for example, a suitable method, suchas rough surfacing treatment method by sandblasting or embossing and amethod of combining transparent fine particle. As a fine particlecombined in order to form a fine concavo-convex structure on theabove-mentioned surface, transparent fine particles whose averageparticle size is 0.5 to 50 μm, for example, such as inorganic type fineparticles that may have conductivity comprising silica, alumina,titania, zirconia, tin oxides, indium oxides, cadmium oxides, antimonyoxides, etc., and organic type fine particles comprising cross-linked ofnon-cross-linked polymers may be used. When forming fine concavo-convexstructure on the surface, the amount of fine particle used is usuallyabout 2 to 50 weight parts to the transparent resin 100 weight partsthat forms the fine concavo-convex structure on the surface, andpreferably 5 to 25 weight parts. An anti glare layer may serve as adiffusion layer (viewing angle expanding function etc.) for diffusingtransmitting light through the polarizing plate and expanding a viewingangle etc.

In addition, the above-mentioned antireflection layer, stickingprevention layer, diffusion layer, anti glare layer, etc. may be builtin the transparent protective film itself, and also they may be preparedas an optical layer different from the transparent protective film.

No specific limitation is placed on an adhesive used in adhesion of atransparent protective film to a polarizer, but a polyvinylalcohol-based adhesive is preferably used. A polyvinyl alcohol-basedadhesive usually contains a polyvinyl alcohol-based resin and acrosslinking agent. However, in a case where an aqueous solutioncontaining a crosslinking agent is used as an aqueous liquid, acrosslinking agent may be contained or is unnecessary to be contained inan adhesive.

Exemplified as polyvinyl alcohol-based resins are a polyvinyl alcoholresin and a polyvinyl alcohol resin having an acetoacetyl group. Apolyvinyl alcohol resin having an acetoacetyl group is a polyvinylalcohol-based adhesive having a highly reactive functional group andpreferably improves of durability of a polarizing plate.

Examples of polyvinyl alcohol-based resin include: a polyvinyl alcoholobtained by saponifying a polyvinyl acetate; a derivative thereof; asaponified copolymer of vinyl acetate and a monomer copolymerizabletherewith; and polyvinyl alcohols modified by acetalization,urethanization, etherification, grafting, phosphate esterification andthe like. Examples of the monomers include, unsaturated carboxylic acidssuch as maleic anhydride, fumaric acid, crotonic acid, itaconic acid and(meth) acrylic acid, and esters thereof; α-olefins such as ethylene andpropylene; (meth)allylsulfonic acid or sodium salt thereof,(meth)allylsulfonate; sodium sulfonate (monoalkyl maleate), sodiumdisulfonate (alkyl maleate); N-methylolacrylamide; an alkai salt ofacrylamide alkylsulfonate; N-vinylpyrrolidone, a derivative ofN-vinylpyrrolidone and the like. The polyvinyl alcohol-based resins canbe either used alone or in combination of two kinds or more.

While no specific limitation is imposed on a polyvinyl alcohol-basedresin, an average degree of polymerization is from about 100 to about3000, preferably from 500 to 3000 and an average degree ofsaponification is from about 85 to about 100 mol %, preferably from 90to 100 mol % in consideration of adherence.

A polyvinyl alcohol-based resin having an acetoacetyl group is obtainedby reacting a polyvinyl alcohol-based resin and diketene to each otherwith a known method. Examples of known methods include: a method inwhich a polyvinyl alcohol-based resin is dispersed into a solvent suchas acetic acid, to which diketene is added and a method in which apolyvinyl alcohol-based resin is previously dissolved into a solventsuch as dimethylformamide or dioxane, to which diketene is added.Another example is a method in which diketene gas or diketene liquid isbrought into direct contact with a polyvinyl alcohol.

No specific limitation is imposed on a degree of modification by anacetoacetyl group in a polyvinyl alcohol-based resin having anacetoacetyl group or groups as far as the degree of modification is 0.1mol % or more. If the degree of modification is less than 0.1 mol %,water resistance of an adhesive layer is insufficient, which isimproper. A degree of modification by an acetoacetyl group is preferablyfrom about 0.1 to about 40 mol %, more preferably from 1 to 20 mol %,further preferably from 2 to 7 mol %. If a degree of modification by anacetoacetyl group exceeds 40 mol %, reaction sites with a crosslinkingagent is fewer to thereby reduce an effect of improvement on waterresistance. A degree of modification by an acetoacetyl group is a valuedetermined with NMR.

Any of crosslinking agents that have been used in a polyvinylalcohol-based adhesive can be used as a crosslinking agent in theinvention without a specific limitation thereon. A crosslinking agentthat can be used is a compound having at least two functional groupshaving reactivity with a polyvinyl alcohol-based resin. Examples thereofinclude: alkylene diamines having an alkylene group and two amino groupssuch as ethylene diamine, triethylene diamine and hexamethylene diamine;isocyanates such as tolylene diisocyanate, hydrogenated tolylenediisocyanate, trimethylolpropane tolylene diisocyanate adduct,triphenylmethane triisocyanate, methylenebis(4-phenylmethane)triisocyanate and isophorone diisocyanate, and ketoxime-blocked productsthereof or isocyanates of phenol-blocked products; epoxy compounds suchas ethylene glycol diglycidyl ether, polyethylene glycol diglycidylether, glycerin di- or triglicydyl ether, 1,6-hexanediol diglycidylether, trimethylolpropane triglycidyl ether, diglicidyl aniline anddiglycidyl amine; monoaldehydes such as formaldehyde, acetaldehyde,propionaldehyde and butylaldehyde; dialdehydes such as glyoxal,malonaldehyde, succindialdehyde, glutardialdehyde, maleic dialdehyde andphthaldialdehyde; amino-formaldehyde resins such as condensates withformaldehyde of methylolurea, methylolmelamine, alkylated methylolurea,alkylated methylolmelamine, acetoguanamine and benzoguanamine; salts ofdivalent metals or trivalent metals such as sodium, potassium,magnesium, calcium, aluminum, iron and nickel, and oxides of the metals.

A mixing quantity of a crosslinking agent described above is usually inthe range of about 0.1 to 35 parts by weight and preferably in the rangeof 10 to 25 parts by weight relative to 100 parts by weight of apolyvinyl alcohol-based resin. In the range, a polarizing plate can beobtained with uniform polarization characteristics and excellency indurability.

On the other hand, in order to further improve durability, acrooslinking agent can be mixed in the range of more than 30 parts byweight and 46 parts by weight or less relative to 100 parts by weight ofa polyvinyl alcohol-based resin into the resin. Especially, in a casewhere polyvinyl alcohol-based resin having an acetoacetyl group isemployed, an amount of a crosslinking agent to be used is preferablymore than 30 parts by weight. By mixing a crosslinking agent in therange of more than 30 parts by weight and 46 parts by weight or less, awater resistance can be drastically improved. A more mixing quantity ofa croslinking agent is more preferable in the above-mentioned range anda mixing quantity thereof is preferably equal to or more than 31 partsby weight, more preferably equal to or more than 32 parts by weight andespecially preferably equal to or more than 35 parts by weight. On theother hand, if a mixing quantity thereof is excessively more, a reactionof a crosslinking agent progresses in a short time to cause an adhesiveto have a trend to gelation. As a result, a pot life as an adhesive isreduced to the extremity and the adhesive has difficulty using in theindustrial aspect. From such a viewpoint, a mixing quantity of acrosslinking agent is preferably 46 parts by weight or less, morepreferably 45 parts by weight or less and especially preferably 40 partsby weight or less.

An adhesive described above (including a case where a polyvinylalcohol-based adhesive and a crosslinking agent are contained) isusually used as an aqueous solution. No specific limitation is placed ona concentration in an aqueous solution, but, in consideration ofcoatability and storage stability, a concentration thereof is usually inthe range of 0.1 to 15 wt %, preferably in the range of 0.5 to 10 wt %and more preferably in the range of about 0.5 to 2 wt %. As aconcentration in a solution is higher, a viscosity increases to thereby,easily generate stripe-shaped appearance irregularity. If aconcentration therein is excessively lower, a viscosity is lowered tothereby render coatability worsened.

Note that various additives described below can be further mixed into anadhesive: coupling agents such as a silane coupling agent and a titaniumcoupling agent; various kinds of tackifiers; an ultraviolet absorbent;an antioxidant; stabilizers such as a heat resistance stabilizer and ahydrolysis resistance stabilizer; and the like.

Note that in a method for manufacturing a polarizing plate in the casewhere an adhesive containing a crosslinking agent in the range of morethan 30 parts by weight and 46 parts by weight or less relative to 100parts by weight of polyvinyl alcohol-based resin containing anacetoacetyl group is used, the adhesive is preferably prepared within 4hr before coating the adhesive. There is a tendency of gelation in anadhesive obtained by mixing a crosslinking agent into polyvinylalcohol-based resin containing an acetoacetyl group after being left asit is for a long time. Hence, an adhesive is preferably prepared in theshortest possible time before coating the adhesive. An adhesive ispreferably prepared within 4 hr before coating the adhesive. An adhesiveis more preferably prepared within 3 hr and especially preferablyprepared within 30 min before coating the adhesive.

In a method for manufacturing a polarizing plate of the invention, anadhesive is coated on a surface of a transparent protective film onwhich an adhesive layer is formed or/and on a surface of a polarizer onwhich an adhesive layer is formed to thereby form an adhesive layer. Athickness of an adhesive layer affects water resistance and wet heatresistance, and with increase in thickness of an adhesive layer,durability is improved. With increase in a thickness of an adhesivelayer, a solution with a higher viscosity is required in a manufacturingprocess therefor, therefore accompanying non-uniformity, especiallygeneration of stripe-shaped appearance faults due to physical stressacting in a PVA-based polarizer. From such a viewpoint, a thickness ofan adhesive layer is preferably in the range of 30 to 300 nm. Athickness of an adhesive layer is more preferably in the range of 60 to250 nm. If a thickness thereof is less than 30 nm, a case arises wherecoating is difficult or an appearance fault is easily generated. On theother hand, if a thickness thereof exceeds 300 mm, appearance faults areeasily generated and durability is unpreferably degraded.

An adhesive described above may be coated on either a transparentprotective film or a polarizer, or both of them. An adhesive ispreferably coated to a thickness in the range of about 30 to 300 nmafter drying.

No specific limitation is placed on a coating operation and any ofvarious kinds of means such as a roll method, a spray method, animmersion method and the like may be employed. After coating anadhesive, a drying step is applied to thereby form an adhesive layer,which is a dry coat layer. A drying temperature is usually in the rangeof about 5 to 150° C., preferably in the range of about 30 to 120° C.and a time of drying is usually 120 sec or more, and preferably 300 secor more.

The adhesive is preferably controlled on temperature in a period frompreparation till coating. Water resistance can be improved bycontrolling a temperature of an adhesive. A controlled temperature of anadhesive is preferably in the range of 30 to 50° C. A controlledtemperature of an adhesive is more preferably in the range of 30 to 45°C. and further more preferably in the range of 30 to 40° C. A controlledtemperature of an adhesive is preferably 30° C. or higher with respectto water resistance. If a controlled temperature exceeds 50° C.,gelation easily occurs immediately after a crosslinking agent is mixed,which makes usage of an adhesive as such difficult. A temperaturecontrol of an adhesive is especially effective in a case of usage of anadhesive containing a crosslinking agent in the range of more than 30parts by weight and 46 parts by weight or less relative to 100 parts byweight of polyvinyl alcohol-based resin containing an acetoacetyl group.

Note that as described above, in a case of usage of an adhesivecontaining a crosslinking agent in the range of more than 30 parts byweight and 46 parts by weight or less relative to 100 parts by weight ofpolyvinyl alcohol-based resin containing an acetoacetyl group, theadhesive is preferably prepared within 4 hr before coating of theadhesive. An operation from preparation of an adhesive till coatingthereof in a short time within 4 hr can be accomplished by incorporatinga step of preparing an adhesive into a series of steps of amanufacturing process for a polarizing plate as a part or by installinga proper preparation apparatus.

Then, in a manufacturing method of the invention, a transparentprotective film and a polarizer are continuously adhered to each otherwith an adhesive layer interposed therebetween. An adhesive layer isformed on a surface of at least one of the transparent protective filmand the polarizer in advance.

No specific limitation is placed on an adhesion method. For example, amethod can be used in which a transparent protective film and apolarizer are caused to continuously pass through between rolls in apair with an adhesive layer interposed therebetween. Such a method isshown in FIGS. 1 to 2. FIG. 1 shows a case where a transparentprotective film 2 on one surface of which an adhesive layer 3 isprovided is caused to pass through between rolls R to thereby adhere toone surface of a polarizer 1 and thereafter, a transparent protectivefilm 2 on which an adhesive layer 3 is provided is adhered to the othersurface of the polarizer 1 in a similar way. On the other hand, FIG. 2shows a case where transparent protective films 2 on each of which anadhesive layer 3 is provided are adhered to both surfaces of a polarizer1 by causing the films to pass through between rolls R.

No specific limitation is place on a pair of rolls R as far as when apolarizer 1 and a transparent protective film 2 on which an adhesivelayer 3 is formed are caused to pass through between the pair of rolls,the films can be adhered to each other under a roll pressure. Forexample, a pair of laminate nip rolls is used. A material of the rollsis not specifically limited and any roll of rubber and a metal may beused.

No specific limitation is placed on a transport velocity of acombination of a transparent protective film and a polarizer (anadhesive layer is formed on a surface of at least one thereof), but atransport velocity thereof is usually in the range of about 0.03 to 0.6m/s, preferably in the range of about 0.08 to 0.5 m/s and morepreferably in the range of about 0.11 to 0.34 m/s.

In a manufacturing method of the invention, an aqueous liquid is causedto be present on an adhering surface when a transparent protective filmand a polarizer are adhered to each other with an adhesive layerinterposed therebetween.

For example, water is used as an aqueous liquid. Pure water ispreferable as the water. An aqueous solution containing a crosslinkingagent dissolved therein is used as an aqueous liquid. A crosslinkingagent to be used is one adapted for a kind of an adhesive. In a case ofusage of a polyvinyl alcohol-based adhesive, a methylol compound ispreferable as a crosslinking agent. No specific limitation is placed ona content of a crosslinking agent, but content thereof is usually 40 wt% or less, preferably in the range of 5 to 40 wt % and more preferablyin the range of 10 to 35 wt %. Note that in a case where an aqueoussolution containing a crosslinking agent is used as an aqueous liquid,an amount of a crosslinking agent is usually in the range of 2 to 40 wt% and preferably in the range of 4 to 35 wt % since a crosslinking agentis more effective in a less content than a case where the crosslinkingagent is contained in an adhesive. In a case where an aqueous solutioncontaining a crosslinking agent is used as an aqueous liquid, nonecessity arises for adding a crosslinking agent into an adhesivesolution, thereby enabling a pot life of the adhesive to be considerablylonger. Such a construction is effective in a case where an adhesivedescribed above is a polyvinyl alcohol-based resin containing anacetoacetyl group, which is a highly reactive functional group.

A viscosity of an aqueous liquid is usually in the range of 0.1 to 10 cPand preferably in the range of 0.5 to 5 cP. A viscosity of an aqueousliquid is a value measured by means of a method described in Example. Ifa viscosity thereof is less than 0.1 cP, a case arises where coating isdifficult, while on the other hand, if a viscosity thereof exceeds 10cP, appearance faults easily occur.

A supply quantity of an aqueous liquid is properly adjusted depending ona transport velocity or the like and is usually in the range of about0.5 to 3.4 ml/s and preferably in the range of 0.5 to 1.7 ml/s. A supplyquantity of an aqueous liquid can be properly adjusted so as to beadapted for the width of a raw material film.

No specific limitation is imposed on a supply method for an aqueousliquid as far as the aqueous liquid is present on an adhering surface ofa transparent protective film and a polarizer when the transparentprotective film and the polarizer are adhered to each other with anadhesive layer interposed therebetween. For example, an aqueous liquidcan be supplied to an adhering surface of the transparent protectivefilm and the polarizer. By supplying an aqueous liquid immediatelybefore adhesion to an adhering surface just before adhesion, durabilityof the adhesive is raised and stripe-shaped appearance faults is moredifficult in generation since the adhesive layer is not brought intocontact with the aqueous liquid till just before adhesion, which ispreferable.

By supplying an aqueous liquid to a transparent protective film or apolarizer (an adhesive layer is formed on at least one thereof) intransport, the aqueous liquid can be guided to an adhering surfacethereof while being transported.

In the invention, it is preferable that an adhesive is coated only onthe transparent protective film side and an aqueous liquid is suppliedon the adhesive layer formed by the coating to thereby cause the aqueousliquid to be present on the adhering surfaces thereof. Especially, sucha case is preferable where transparent protective films are adhered ontoboth surfaces of a polarizer in a state as shown in FIG. 2. This isbecause, in the example of FIG. 2, an unfavorable possibility occursthat the adhesive drip if an adhesive layer is provided on the polarizerside. It is preferable, because of the same reason, to supply an aqueousliquid on adhesive layers formed on transparent protective films.

In a case where an adhesive is coated only on the transparent protectivefilm sides to form adhesive layers, an aqueous liquid can be supplied tothe polarizer side. According to such a method, the adhesive layer isnot brought into contact with the aqueous liquid by just before adhesionin a similar way to that as described above. If a moisture percentage inthe inside or on the surface of a polarizer is smaller, this situationcontributes to generation of stripe-shaped appearance faults. On theother hand, if a moisture percentage of the polarizer is raised,stripe-shaped appearance faults is difficult to be generated. If anaqueous liquid is supplied to the polarizer side, a moisture percentageof the polarizer is raised in a period till the polarizer is guided toadhesion rolls from a position of supply of the aqueous liquid, therebyenabling generation of stripe-shaped appearance faults to be effectivelysuppressed.

In a case where adhesive layers are formed by coating an adhesive onlyon the polarizer side, an aqueous liquid is preferably supplied to thetransparent protective film sides. According to such a method, theadhesive layers are not brought into contact with the aqueous liquid byjust before adhesion in a similar way to that as described above. Supplyof an aqueous liquid to transparent protective films is advantageous interms of a manufacturing apparatus since transparent protective filmscan be continuously adhered simultaneously on both surfaces of apolarizer without dripping of the adhesive.

In a case where transparent protective films and a polarizer arecontinuously adhered to each other with an adhesive layer interposedthere between, an aqueous liquid is preferably supplied to adheringsurfaces just before adhesion. The term “just before adhesion” means toadhere in a short time of 30 sec or less from supply of the aqueousliquid. The shorter the time is, the better a result is and a time toadhesion from the supply of an aqueous liquid is usually 5 sec or less,preferably 2 sec or less, more preferably 1 sec and further morepreferably 0.5 sec or less. If a time to adhesion is excessive long, theadhesive is dissolved more than necessary in a case where the aqueousliquid is supplied on the adhesive layer, which easily causes anappearance irregularity. In a case where an aqueous liquid is suppliedon transparent protective films or a polarizer, a moisture percentage isexcessive large, therefore rendering appearance irregularity easilyobserved after drying. In a case where an aqueous liquid is suppliedjust before adhesion in such a way, a place on which the aqueous liquidis supplied may be either on the transparent protective film sides, oron one surface side or both sides of the polarizer. Alternatively, amethod may also be used in which a liquid pool is provided in anadhesion section, and transparent protective films and/or a polarizerpasses through the liquid pool just before adhesion.

In FIGS. 1 and 2, an aqueous liquid 4 is supplied to adhering surfacesbetween adhesive layers 3 provided to transparent protective film 2 anda polarizer 1. In FIGS. 1 and 2, an aqueous liquid has only to bepresent between rolls R in a pair and a site at which the aqueous liquid4 is provided can be appropriately altered. In FIGS. 1 and 2, one supplysite of the aqueous liquid 4 is provided to a pair of transported films(a combination of the polarizer and the transparent protective films),but plural supply sites of the aqueous liquid 4 can be provided. Asupply site of an aqueous liquid 4 can also be provided to each pair oftransported films. Methods for supplying an aqueous liquid include, forexample, a dropping method, a coating method, a spray method and thelike. A nozzle, a sprayer, a coater or the like can be selectively usedin the supply methods.

In a case where an aqueous liquid is excessively present on adheringsurfaces between transparent protective films and a polarizer and runsout from an edge portion of the adhering surfaces, the aqueous liquid inexcess is removed with a suction nozzle or the like or gathered to acentral portion of each of the adhering surfaces with an air nozzle orthe like to thereby enable contamination due to running-out of theaqueous liquid to be prevented.

After the polarizer and the transparent protective films are adhered toeach other with the adhesive layer interposed therebetween in thepresence of the aqueous liquid with a roll laminator or the like asdescribed above, the combination of the polarizer and the transparentprotective are subjected to a drying step. A drying temperature isusually in the range of about 5 to 150° C. and preferably in the rangeof 30 to 120° C. for a time of 120 sec or more and preferably 300 sec ormore.

A polarizing plate of the present invention may be used in practical useas an optical film laminated with other optical layers. Although thereis especially no limitation about the optical layers, one layer or twolayers or more of optical layers, which may be used for formation of aliquid crystal display etc., such as a reflector, a transflective plate,a retardation plate (a half wavelength plate and a quarter wavelengthplate included), and a viewing angle compensation film, may be used.Especially preferable polarizing plates are; a reflection typepolarizing plate or a transflective type polarizing plate in which areflector or a transflective reflector is further laminated onto apolarizing plate of the present invention; an elliptically polarizingplate or a circular polarizing plate in which a retardation plate isfurther laminated onto the polarizing plate; a wide viewing anglepolarizing plate in which a viewing angle compensation film is furtherlaminated onto the polarizing plate; or a polarizing plate in which abrightness enhancement film is further laminated onto the polarizingplate.

A reflective layer is prepared on a polarizing plate to give areflection type polarizing plate, and this type of plate is used for aliquid crystal display in which an incident light from a view side(display side) is reflected to give a display. This type of plate doesnot require built-in light sources, such as a backlight, but has anadvantage that a liquid crystal display may easily be made thinner. Areflection type polarizing plate may be formed using suitable methods,such as a method in which a reflective layer of metal etc. is, ifrequired, attached to one side of a polarizing plate through atransparent protective film etc.

As an example of a reflection type polarizing plate, a plate may bementioned on which, if required, a reflective layer is formed using amethod of attaching a foil and vapor deposition film of reflectivemetals, such as aluminum, to one side of a matte treated transparentprotective film. Moreover, a different type of plate with a fineconcavo-convex structure on the surface obtained by mixing fine particleinto the above-mentioned transparent protective film, on which areflective layer of concavo-convex structure is prepared, may bementioned. The reflective layer that has the above-mentioned fineconcavo-convex structure diffuses incident light by random reflection toprevent directivity and glaring appearance, and has an advantage ofcontrolling unevenness of light and darkness etc. Moreover, thetransparent protective film containing the fine particle has anadvantage that unevenness of light and darkness may be controlled moreeffectively, as a result that an incident light and its reflected lightthat is transmitted through the film are diffused. A reflective layerwith fine concavo-convex structure on the surface effected by a surfacefine concavo-convex structure of a transparent protective film may beformed by a method of attaching a metal to the surface of a transparentprotective layer directly using, for example, suitable methods of avacuum evaporation method, such as a vacuum deposition method, an ionplating method, and a sputtering method, and a plating method etc.

Instead of a method in which a reflection plate is directly given to thetransparent protective film of the above-mentioned polarizing plate, areflection plate may also be used as a reflective sheet constituted bypreparing a reflective layer on the suitable film for the transparentfilm. In addition, since a reflective layer is usually made of metal, itis desirable that the reflective side is covered with a transparentprotective film or a polarizing plate etc. when used, from a viewpointof preventing deterioration in reflectance by oxidation, of maintainingan initial reflectance for a long period of time and of avoidingpreparation of a protective layer separately etc.

In addition, a transflective type polarizing plate may be obtained bypreparing the above-mentioned reflective layer as a transflective typereflective layer, such as a half-mirror etc. that reflects and transmitslight. A transflective type polarizing plate is usually prepared in thebackside of a liquid crystal cell and it may form a liquid crystaldisplay unit of a type in which a picture is displayed by an incidentlight reflected from a view side (display side) when used in acomparatively well-lighted atmosphere. And this unit displays a picture,in a comparatively dark atmosphere, using embedded type light sources,such as a back light built in backside of a transflective typepolarizing plate. That is, the transflective type polarizing plate isuseful to obtain of a liquid crystal display of the type that savesenergy of light sources, such as a back light, in a well-lightedatmosphere, and can be used with a built-in light source if needed in acomparatively dark atmosphere etc.

The above-mentioned polarizing plate may be used as ellipticallypolarizing plate or circularly polarizing plate on which the retardationplate is laminated. A description of the above-mentioned ellipticallypolarizing plate or circularly polarizing plate will be made in thefollowing paragraph. These polarizing plates change linearly polarizedlight into elliptically polarized light or circularly polarized light,elliptically polarized light or circularly polarized light into linearlypolarized light or change the polarization direction of linearlypolarization by a function of the retardation plate. As a retardationplate that changes circularly polarized light into linearly polarizedlight or linearly polarized light into circularly polarized light, whatis called a quarter wavelength plate (also called λ/4 plate) is used.Usually, half-wavelength plate (also called λ/2 plate) is used, whenchanging the polarization direction of linearly polarized light.

Elliptically polarizing plate is effectively used to give a monochromedisplay without above-mentioned coloring by compensating (preventing)coloring (blue or yellow color) produced by birefringence of a liquidcrystal layer of a super twisted nematic (STN) type liquid crystaldisplay. Furthermore, a polarizing plate in which three-dimensionalrefractive index is controlled may also preferably compensate (prevent)coloring produced when a screen of a liquid crystal display is viewedfrom an oblique direction. Circularly polarizing plate is effectivelyused, for example, when adjusting a color tone of a picture of areflection type liquid crystal display that provides a colored picture,and it also has function of antireflection. For example, a retardationplate may be used that compensates coloring and viewing angle, etc.caused by birefringence of various wavelength plates or liquid crystallayers etc. Besides, optical characteristics, such as retardation, maybe controlled using laminated layer with two or more sorts ofretardation plates having suitable retardation value according to eachpurpose. As retardation plates, birefringence films formed by stretchingfilms comprising suitable polymers, such as polycarbonates, norbornenetype resins, polyvinyl alcohols, polystyrenes, poly methylmethacrylates, polypropylene; polyarylates and polyamides; aligned filmscomprising liquid crystal materials, such as liquid crystal polymer; andfilms on which an alignment layer of a liquid crystal material issupported may be mentioned. A retardation plate may be a retardationplate that has a proper retardation according to the purposes of use,such as various kinds of wavelength plates and plates aiming atcompensation of coloring by birefringence of a liquid crystal layer andof visual angle, etc., and may be a retardation plate in which two ormore sorts of retardation plates is laminated so that opticalproperties, such as retardation, may be controlled.

The above-mentioned elliptically polarizing plate and an above-mentionedreflected type elliptically polarizing plate are laminated platecombining suitably a polarizing plate or a reflection type polarizingplate with a retardation plate. This type of elliptically polarizingplate etc. may be manufactured by combining a polarizing plate(reflected type) and a retardation plate, and by laminating them one byone separately in the manufacture process of a liquid crystal display.On the other hand, the polarizing plate in which lamination wasbeforehand carried out and was obtained as an optical film, such as anelliptically polarizing plate, is excellent in a stable quality, aworkability in lamination etc., and has an advantage in improvedmanufacturing efficiency of a liquid crystal display.

A viewing angle compensation film is a film for extending viewing angleso that a picture may look comparatively clearly, even when it is viewedfrom an oblique direction not from vertical direction to a screen. Assuch a viewing angle compensation retardation plate, in addition, a filmhaving birefringence property that is processed by uniaxial stretchingor orthogonal biaxial stretching and a biaxial stretched film asinclined alignment film etc. may be used. As inclined alignment film,for example, a film obtained using a method in which a heat shrinkingfilm is adhered to a polymer film, and then the combined film is heatedand stretched or shrunk under a condition of being influenced by ashrinking force, or a film that is aligned in oblique direction may bementioned. The viewing angle compensation film is suitably combined forthe purpose of prevention of coloring caused by change of visible anglebased on retardation by liquid crystal cell etc. and of expansion ofviewing angle with good visibility.

Besides, a compensation plate in which an optical anisotropy layerconsisting of an alignment layer of liquid crystal polymer, especiallyconsisting of an inclined alignment layer of discotic liquid crystalpolymer is supported with triacetyl cellulose film may preferably beused from a viewpoint of attaining a wide viewing angle with goodvisibility.

The polarizing plate with which a polarizing plate and a brightnessenhancement film are adhered together is usually used being prepared ina backside of a liquid crystal cell. A brightness enhancement film showsa characteristic that reflects linearly polarized light with apredetermined polarization axis, or circularly polarized light with apredetermined direction, and that transmits other light, when naturallight by back lights of a liquid crystal display or by reflection from aback-side etc., comes in. The polarizing plate, which is obtained bylaminating a brightness enhancement film to a polarizing plate, thusdoes not transmit light without the predetermined polarization state andreflects it, while obtaining transmitted light with the predeterminedpolarization state by accepting a light from light sources, such as abacklight. This polarizing plate makes the light reflected by thebrightness enhancement film further reversed through the reflectivelayer prepared in the backside and forces the light re-enter into thebrightness enhancement film, and increases the quantity of thetransmitted light through the brightness enhancement film bytransmitting a part or all of the light as light with the predeterminedpolarization state. The polarizing plate simultaneously suppliespolarized light that is difficult to be absorbed in a polarizer, andincreases the quantity of the light usable for a liquid crystal picturedisplay etc., and as a result luminosity may be improved. That is, inthe case where the light enters through a polarizer from backside of aliquid crystal cell by the back light etc. without using a brightnessenhancement film, most of the light, with a polarization directiondifferent from the polarization axis of a polarizer, is absorbed by thepolarizer, and does not transmit through the polarizer. This means thatalthough influenced with the characteristics of the polarizer used,about 50 percent of light is absorbed by the polarizer, the quantity ofthe light usable for a liquid crystal picture display etc. decreases somuch, and a resulting picture displayed becomes dark. A brightnessenhancement film does not enter the light with the polarizing directionabsorbed by the polarizer into the polarizer but reflects the light onceby the brightness enhancement film, and further makes the light reversedthrough the reflective layer etc. prepared in the backside to re-enterthe light into the brightness enhancement film. By this above-mentionedrepeated operation, only when the polarization direction of the lightreflected and reversed between the both becomes to have the polarizationdirection which may pass a polarizer, the brightness enhancement filmtransmits the light to supply it to the polarizer. As a result, thelight from a backlight may be efficiently used for the display of thepicture of a liquid crystal display to obtain a bright screen.

A diffusion plate may also be prepared between brightness enhancementfilm and the above described reflective layer, etc. A polarized lightreflected by the brightness enhancement film goes to the above describedreflective layer etc., and the diffusion plate installed diffusespassing light uniformly and changes the light state into depolarizationat the same time. That is, the diffusion plate returns polarized lightto natural light state. Steps are repeated where light, in theunpolarized state, i.e., natural light state, reflects throughreflective layer and the like, and again goes into brightnessenhancement film through diffusion plate toward reflective layer and thelike. Diffusion plate that returns polarized light to the natural lightstate is installed between brightness enhancement film and the abovedescribed reflective layer, and the like, in this way, and thus auniform and bright screen may be provided while maintaining brightnessof display screen, and simultaneously controlling non-uniformity ofbrightness of the display screen. By preparing such diffusion plate, itis considered that number of repetition times of reflection of a firstincident light increases with sufficient degree to provide uniform andbright display screen conjointly with diffusion function of thediffusion plate.

The suitable films are used as the above-mentioned brightnessenhancement film. Namely, multilayer thin film of a dielectricsubstance; a laminated film that has the characteristics of transmittinga linearly polarized light with a predetermined polarizing axis, and ofreflecting other light, such as the multilayer laminated film of thethin film having a different refractive-index anisotropy; an alignedfilm of cholesteric liquid-crystal polymer; a film that has thecharacteristics of reflecting a circularly polarized light with eitherleft-handed or right-handed rotation and transmitting other light, suchas a film on which the aligned cholesteric liquid crystal layer issupported; etc. may be mentioned.

Therefore, in the brightness enhancement film of a type that transmits alinearly polarized light having the above-mentioned predeterminedpolarization axis, by arranging the polarization axis of the transmittedlight and entering the light into a polarizing plate as it is, theabsorption loss by the polarizing plate is controlled and the polarizedlight can be transmitted efficiently. On the other hand, in thebrightness enhancement film of a type that transmits a circularlypolarized light as a cholesteric liquid-crystal layer, the light may beentered into a polarizer as it is, but it is desirable to enter thelight into a polarizer after changing the circularly polarized light toa linearly polarized light through a retardation plate, taking controlan absorption loss into consideration. In addition, a circularlypolarized light is convertible into a linearly polarized light using aquarter wavelength plate as the retardation plate.

A retardation plate that works as a quarter wavelength plate in a widewavelength ranges, such as a visible-light band, is obtained by a methodin which a retardation layer working as a quarter wavelength plate to apale color light with a wavelength of 550 nm is laminated with aretardation layer having other retardation characteristics, such as aretardation layer working as a half-wavelength plate. Therefore, theretardation plate located between a polarizing plate and a brightnessenhancement film may consist of one or more retardation layers.

In addition, also in a cholesteric liquid-crystal layer, a layerreflecting a circularly polarized light in a wide wavelength ranges,such as a visible-light band, may be obtained by adopting aconfiguration structure in which two or more layers with differentreflective wavelength are laminated together. Thus a transmittedcircularly polarized light in a wide wavelength range may be obtainedusing this type of cholesteric liquid-crystal layer.

Moreover, the polarizing plate may consist of multi-layered film oflaminated layers of a polarizing plate and two of more of optical layersas the above-mentioned separated type polarizing plate. Therefore, apolarizing plate may be a reflection type elliptically polarizing plateor a semi-transmission type elliptically polarizing plate, etc. in whichthe above-mentioned reflection type polarizing plate or a transflectivetype polarizing plate is combined with above described retardation platerespectively.

Although an optical film with the above described optical layerlaminated to the polarizing plate may be formed by a method in whichlaminating is separately carried out sequentially in manufacturingprocess of a liquid crystal display etc., an optical film in a form ofbeing laminated beforehand has an outstanding advantage that it hasexcellent stability in quality and assembly workability, etc., and thusmanufacturing processes ability of a liquid crystal display etc. may beraised. Proper adhesion means, such as an adhesive layer, may be usedfor laminating. On the occasion of adhesion of the above describedpolarizing plate and other optical films, the optical axis may be set asa suitable configuration angle according to the target retardationcharacteristics etc.

In the polarizing plate mentioned above and the optical film in which atleast one layer of the polarizing plate is laminated, an adhesive layermay also be prepared for adhesion with other members, such as a liquidcrystal cell etc. As pressure sensitive adhesive that forms adhesivelayer is not especially limited, and, for example, acrylic typepolymers; silicone type polymers; polyesters, polyurethanes, polyamides,polyethers; fluorine type and rubber type polymers may be suitablyselected as a base polymer. Especially, a pressure sensitive adhesivesuch as acrylics type pressure sensitive adhesives may be preferablyused, which is excellent in optical transparency, showing adhesioncharacteristics with moderate wettability, cohesiveness and adhesiveproperty and has outstanding weather resistance, heat resistance, etc.

Moreover, an adhesive layer with low moisture absorption and excellentheat resistance is desirable. This is because those characteristics arerequired in order to prevent foaming and peeling-off phenomena bymoisture absorption, in order to prevent decrease in opticalcharacteristics and curvature of a liquid crystal cell caused by thermalexpansion difference etc. and in order to manufacture a liquid crystaldisplay excellent in durability with high quality.

The adhesive layer may contain additives, for example, such as naturalor synthetic resins, adhesive resins, glass fibers, glass beads, metalpowder, fillers comprising other inorganic powder etc., pigments,colorants and antioxidants. Moreover, it may be an adhesive layer thatcontains fine particle and shows optical diffusion nature.

Proper method may be carried out to attach an adhesive layer to one sideor both sides of the optical film. As an example, about 10 to 40 wt % ofthe pressure sensitive adhesive solution in which a base polymer or itscomposition is dissolved or dispersed, for example, toluene or ethylacetate or a mixed solvent of these two solvents is prepared. A methodin which this solution is directly applied on a polarizing plate top oran optical film top using suitable developing methods, such as flowmethod and coating method, or a method in which an adhesive layer isonce formed on a separator, as mentioned above, and is then transferredon a polarizing plate or an optical film may be mentioned.

An adhesive layer may also be prepared on one side or both sides of apolarizing plate or an optical film as a layer in which pressuresensitive adhesives with different composition or different kind etc.are laminated together. Moreover, when adhesive layers are prepared onboth sides, adhesive layers that have different compositions, differentkinds or thickness, etc. may also be used on front side and backside ofa polarizing plate or an optical film. Thickness of an adhesive layermay be suitably determined depending on a purpose of usage or adhesivestrength, etc., and generally is 1 to 500 μm, preferably 5 to 200 μm,and more preferably 10 to 100 μm.

A temporary separator is attached to an exposed side of an adhesivelayer to prevent contamination etc., until it is practically used.Thereby, it can be prevented that foreign matter contacts adhesive layerin usual handling. As a separator, without taking the above-mentionedthickness conditions into consideration, for example, suitableconventional sheet materials that is coated, if necessary, with releaseagents, such as silicone type, long chain alkyl type, fluorine typerelease agents, and molybdenum sulfide may be used. As a suitable sheetmaterial, plastics films, rubber sheets, papers, cloths, no wovenfabrics, nets, foamed sheets and metallic foils or laminated sheetsthereof may be used.

In addition, in the present invention, ultraviolet absorbing propertymay be given to the above-mentioned each layer, such as a polarizer fora polarizing plate, a transparent protective film and an optical filmetc. and an adhesive layer, using a method of adding UV absorbents, suchas salicylic acid ester type compounds, benzophenol type compounds,benzotriazol type compounds, cyano acrylate type compounds, and nickelcomplex salt type compounds.

An optical film of the present invention may be preferably used formanufacturing various equipment, such as liquid crystal display, etc.Assembling of a liquid crystal display may be carried out according toconventional methods. That is, a liquid crystal display is generallymanufactured by suitably assembling several parts such as a liquidcrystal cell, optical films and, if necessity, lighting system, and byincorporating driving circuit. In the present invention, except that anoptical film by the present invention is used, there is especially nolimitation to use any conventional methods. Also any liquid crystal cellof arbitrary type, such as TN type, and STN type, π type may be used.

Suitable liquid crystal displays, such as liquid crystal display withwhich the above-mentioned optical film has been located at one side orboth sides of the liquid crystal cell, and with which a backlight or areflector is used for a lighting system may be manufactured. In thiscase, the optical film by the present invention may be installed in oneside or both sides of the liquid crystal cell. When installing theoptical films in both sides, they may be of the same type or ofdifferent type. Furthermore, in assembling a liquid crystal display,suitable parts, such as diffusion plate, anti-glare layer,antireflection film, protective plate, prism array, lens array sheet,optical diffusion plate, and backlight, may be installed in suitableposition in one layer or two or more layers.

Subsequently, organic electro luminescence equipment (organic ELdisplay) will be explained. Generally, in organic EL display, atransparent electrode, an organic emitting layer and a metal electrodeare laminated on a transparent substrate in an order configuring anilluminant (organic electro luminescence illuminant). Here, an organicemitting layer is a laminated material of various organic thin films,and much compositions with various combination are known, for example, alaminated material of hole injection layer comprising triphenylaminederivatives etc., a luminescence layer comprising fluorescent organicsolids, such as anthracene; a laminated material of electronic injectionlayer comprising such a luminescence layer and perylene derivatives,etc.; laminated material of these hole injection layers, luminescencelayer, and electronic injection layer etc.

An organic EL display emits light based on a principle that positivehole and electron are injected into an organic emitting layer byimpressing voltage between a transparent electrode and a metalelectrode, the energy produced by recombination of these positive holesand electrons excites fluorescent substance, and subsequently light isemitted when excited fluorescent substance returns to ground state. Amechanism called recombination which takes place in a intermediateprocess is the same as a mechanism in common diodes, and, as isexpected, there is a strong non-linear relationship between electriccurrent and luminescence strength accompanied by rectification nature toapplied voltage.

In an organic EL display, in order to take out luminescence in anorganic emitting layer, at least one electrode must be transparent. Thetransparent electrode usually formed with transparent electricconductor, such as indium tin oxide (ITO), is used as an anode. On theother hand, in order to make electronic injection easier and to increaseluminescence efficiency, it is important that a substance with smallwork function is used for cathode, and metal electrodes, such as Mg—Agand Al—Li, are usually used.

In organic EL display of such a configuration, an organic emitting layeris formed by a very thin film about 10 nm in thickness. For this reason,light is transmitted nearly completely through organic emitting layer asthrough transparent electrode. Consequently, since the light thatenters, when light is not emitted, as incident light from a surface of atransparent substrate and is transmitted through a transparent electrodeand an organic emitting layer and then is reflected by a metalelectrode, appears in front surface side of the transparent substrateagain, a display side of the organic EL display looks like mirror ifviewed from outside.

In an organic EL display containing an organic electro luminescenceilluminant equipped with a transparent electrode on a surface side of anorganic emitting layer that emits light by impression of voltage, and atthe same time equipped with a metal electrode on a back side of organicemitting layer, a retardation plate may be installed between thesetransparent electrodes and a polarizing plate, while preparing thepolarizing plate on the surface side of the transparent electrode.

Since the retardation plate and the polarizing plate have functionpolarizing the light that has entered as incident light from outside andhas been reflected by the metal electrode, they have an effect of makingthe mirror surface of metal electrode not visible from outside by thepolarization action. If a retardation plate is configured with a quarterwavelength plate and the angle between the two polarization directionsof the polarizing plate and the retardation plate is adjusted to π/4,the mirror surface of the metal electrode may be completely covered.

This means that only linearly polarized light component of the externallight that enters as incident light into this organic EL display istransmitted with the work of polarizing plate. This linearly polarizedlight generally gives an elliptically polarized light by the retardationplate, and especially the retardation plate is a quarter wavelengthplate, and moreover when the angle between the two polarizationdirections of the polarizing plate and the retardation plate is adjustedto π/4, it gives a circularly polarized light.

This circularly polarized light is transmitted through the transparentsubstrate, the transparent electrode and the organic thin film, and isreflected by the metal electrode, and then is transmitted through theorganic thin film, the transparent electrode and the transparentsubstrate again, and is turned into a linearly polarized light againwith the retardation plate. And since this linearly polarized light liesat right angles to the polarization direction of the polarizing plate,it cannot be transmitted through the polarizing plate. As the result,mirror surface of the metal electrode may be completely covered.

EXAMPLES

Description will be given below of the construction and effect of theinvention using examples and the like showing them in a concrete manner.Note that the terms “part or parts and %” means units based on weightunless otherwise stated.

(Viscosity Measuring Method for Aqueous Liquid)

A viscosity was measured at a rate of shear of 82000 (1/s) at 23° C.using a viscosity measuring instrument (Rheometer Rheostress 1,manufactured by Thermo Haake Co.).

(Thickness Measuring Method for Adhesive Layer)

A thickness was measured by observation on a section with SEM.

(Preparation of Polarizer (A))

A polyvinyl alcohol (PVA) film with an average polymerization degree of2400, a saponification degree of 99.9 mol % and a thickness of 80 μm wasimmersed into pure water at 25° C. for 60 sec to swell, while uniaxiallystretched in a flow direction to a stretch magnification of 2 times.Then, the uniaxially stretched film was immersed in a 5% aqueoussolution of iodine and potassium iodide at iodine/potassium iodide ratioof 1/10 in wt ratio, while stretched so that a total stretchmagnification of 2.5 times and thereafter, the film is further stretchedin an aqueous solution of boric acid at a concentration of 4 wt % andpotassium iodide at a concentration of 3 wt % at 40° C. to a totalstretch magnification of 3 times. Thereafter, the film was furtherstretched in an aqueous solution of potassium iodide at a concentrationof 5 wt % at 25° C. to a total stretch magnification of 5.5 times,followed by washing in pure water. Then, the film was dried in an ovenat 40° C. for 3 min to obtain a polarizer (A) with a thickness of 30 μm.

(Manufacture of Polarizer (B))

A polarizer (B) with a thickness of 19 μm was obtained in a similar wayto that as described above with the exception that in the manufacture ofa polarizer (A), a PVA film with an average polymerization degree of2400, a saponification degree of 99.9 mol % and a thickness of 50 μm wasused.

(Transparent Protective Film)

A triacetyl cellulose (TAC) film with a thickness of 40 μm was used.

Example 1

(Preparation of Adhesive)

Dissolved into pure water at a temperature of 30° C. were 100 parts of aPVA-based resin containing an acetoacetyl (AA) group (with an averagepolymerization degree of 1200, a saponification degree of 98.5 mol %,and an AA group modification degree of 5 mol %, which is shown as AAmodified PVA in table 1) and 20 parts of methylol melamine to therebyprepare an aqueous solution at an adjusted solid matter concentration of0.5%. The solution was used at a temperature of 30° C. as an adhesive.

(Manufacture of Polarizing Plate (a))

The adhesive was coated with die coater on one surface of thetransparent protective film. The adhesive was coated 30 min after thepreparation. Then, the wet coat was dried at 50° C. for 3 min to form anadhesive layer with a thickness of 31 nm after drying.

Then, TAC films each with the adhesive layer thereon were, as shown inFIG. 2, adhered to both surfaces of the polarizer (A) with a thicknessof 30 μm with a roll machine while pure waters with a viscosity of 1 cP(at 23° C.) were supplied. A film transport velocity was 0.25 m/s and asupply rate of pure waters was 0.80 ml/s. Pure waters were supplied tosites on transparent protective films (at positions where it take 0.5sec to reach the positions of adhesions on the films). Thereafter, thelaminated film was dried for 6 min at 55° C. to thereby manufacture apolarizing plate.

Examples 2 to 4

Polarizing plates were obtained in a similar way to that in Example 1with the exception that in the preparation of the adhesive of Example 1,concentrations of adhesives were varied as shown in Table 1. Thicknessvalues of the adhesive layers are as shown in Table 1.

Examples 5 to 12

Polarizing plates were obtained in a similar way to that in Example 1with the exception that in the preparation of the adhesive of Example 1,kinds of crosslinking agents used in adhesives and concentrations of theadhesives varied as shown in Table 1. Thickness values of the adhesivelayers are as shown in Table 1.

Examples 13 to 16

Polarizing plates were obtained in a similar way to that in Example 1with the exception that in the preparation of the adhesive of Example 1,resins used in adhesives were replaced with a polyvinyl alcohol-basedresin (with an average polymerization degree of 1200 and asaponification degree of 98.5 mol %) and concentrations of the adhesiveswere varied as shown in Table 1. Thickness values of the adhesive layersare shown in Table 1.

Example 17

A polarizing plate was obtained in a similar way to that in Example 1with the exception that in the preparation of the polarizing plate ofExample 1, an aqueous solution containing methylol melamine at aconcentration of 5 wt % with a viscosity of 3 cP (at 23° C.) was usedinstead of pure water. A thickness of an adhesive layer is shown inTable 1.

Examples 18 to 20

Polarizing plates were obtained in a similar way to that in Example 1with the exception that in the preparation of the adhesive of Example 1,the crosslinking agent was not used in adhesives and in the preparationof the polarizing plate of Example 1, an aqueous solution shown in Table1 was used instead of pure water. Thickness values of adhesive layersare shown in Table 1.

Example 21

A polarizing plate was obtained in a similar way to that in Example 3with the exception that in Example 3, the crosslinking agent was notused in the adhesive. A thickness of adhesive layer is shown in Table 1.

Examples 22 to 24

Polarizing plates were obtained in a similar way to that in Example 3with the exception that in Example 3, the crosslinking agent was notused in the adhesive and an aqueous solution shown in Table 1 was usedinstead of pure water. Thickness values of adhesive layers are shown inTable 1.

Example 25

A polarizing plate was obtained in a similar way to that in Example 3with the exception that in Example 3, the crosslinking agent was notused in the adhesive. A thickness of adhesive layer is shown in Table 1.

Examples 26 to 28

Polarizing plates were obtained in a similar way to that in Example 3with the exception that in Example 3, the crosslinking agent was notused in the adhesive and the aqueous solution shown in Table 1 were usedinstead of pure water. Thickness values of adhesive layers are shown inTable 1.

Example 29

A polarizing plate was obtained in a similar way to that in Example 3with the exception that in Example 3, pure waters were supplied in dropson triacetyl cellulose films with the adhesive layer thereon atdistances of 1 m from positions where the films and the polarizer wereadhered to each other instead of the way that pure waters were suppliedin drops on the films just before the adhesions (at positions where ittakes 0.5 sec to reach the positions of adhesions on the films) and atransport velocity of the film was set to 0.25 m/s so that it takes 4sec to reach the positions of the adhesions. A thickness of adhesivelayer is shown in Table 1.

Example 30

A polarizing plate was obtained in a similar way to that in Example 3with the exception that in Example 3, pure waters were supplied in dropson triacetyl cellulose films with the adhesive layer thereon atdistances of 1 m from positions where the films and the polarizer wereadhered to each other instead of the way that pure waters were suppliedin drops on the films just before the adhesions (at positions where ittakes 0.5 sec to reach the positions of adhesions on the films) and atransport velocity of the film was set to 0.1 m/s so that it takes 10sec to reach the positions of the adhesions. A thickness of adhesivelayer is shown in Table 1.

Example 31

A polarizing plate was obtained in a similar way to that in Example 3with the exception that in Example 3, pure waters were supplied in dropson triacetyl cellulose films with the adhesive layer thereon atdistances of 1 m from positions where the films and the polarizer wereadhered to each other instead of the way that pure waters were suppliedin drops on the films just before the adhesions (at a position where ittakes 0.5 sec to reach the positions of adhesions on the films) and atransport velocity of the film was set to 0.04 m/s so that it takes thefilm 25 sec to reach the positions of adhesions. A thickness of adhesivelayer is shown in Table 1.

Example 32

A polarizing plate was obtained in a similar way to that in Example 3with the exception that in Example 3, the polarizer (B) was used insteadof the polarizer (A). A thickness of adhesive layer is shown in Table 1.

Comparative Example 1

A polarizing plate was prepared in a similar way to that in Example 1with the exception that a way of manufacture of polarizing plate (b)described below was employed instead of the way of manufacture ofpolarizing plate (a) in Example 1.

(Manufacture of Polarizing Plate (b))

Transparent protective films were, as shown in FIG. 4, adhered onto bothsurfaces of a polarizer (A) with a roll machine while the adhesive wassupplied, and thereafter, the laminate film was dried at 55° C. for 6min to thereby manufacture a polarizing plate. A transport velocity ofthe transparent protective films was set to 0.35 m/s and a supplyquantity of the adhesive was set to 0.60 ml/s. Supply sites were ontransparent protective films (at positions where it takes 0.5 sec toreach the positions of adhesions on the films) to thereby form adhesivelayers with a thickness of 16 mm after drying on the films.

Comparative Examples 2 to 20

Polarizing plates were obtained in a similar way to that in ComparativeExample 1 with the exception that kinds of polyvinyl alcohol-basedresins used in adhesives, kinds of crosslinking agents andconcentrations of adhesives were varied as shown in Table 1. Thicknessvalues of the adhesives are shown in Table 1. Note that in ComparativeExamples 17 to 20, a polyvinyl alcohol-based resin (with an averagepolymerization degree of 1200 and a saponification degree of 98.5 mol %)was used.

Comparative Example 21

A polarizing plate was obtained in a similar way to that in ComparativeExample 3 with the exception that the polarizer (B) was used instead ofthe polarizer (A). A thickness of adhesive layer is shown in Table 1.

(Evaluation)

The polarizing plates obtained in Examples and Comparative Examples werecut into polarizing plate samples so that a size of each polarizingplate sample is 50 mm in the direction of the absorption axis of thepolarizer and 25 mm in a direction perpendicular to the absorption axis.Evaluation was conducted on the samples with the following criteria. Theresults are shown in Table 1.

(Appearance Fault Evaluation)

Light from a fluorescent lamp was reflected on the obtained polarizingplate sample to visually evaluate a reflection image with the followingcriteria:

∘: any of stripe-shaped or dotted faults and other irregularities is notobserved.

▴: stripe-shaped or dotted faults and other irregularities are observedin a local area.

x : stripe-shaped or dotted faults and other irregularities are observedall over the surface.

(Light Leakage Evaluation)

The obtained two polarizing plate samples were superimposed in thecross-Nichols relation so that the absorption axes are perpendicular toeach other and in this state, light leakage of the superimposed samplesusing light from a fluorescent lamp was visually evaluated with thefollowing criteria:

∘: without light leakage

x : with light leakage

(Durability)

The obtained polarizing plate samples were immersed in warm water at 60°C. for 3 hr and thereafter, a peel length (mm) at an edge of a samplewas measured and evaluated with the following criteria. Measurement of apeel length (mm) was made using a caliper or a square.

∘∘: without a peel

∘: with a peel less than 3 mm

▴: with a peel in the range of 3 to 30 mm

x : with a peel of 31 mm or longer TABLE 1 Adhesives Concen- Kinds oftrations cross- in Thicknesses of Aqueous liquids Evaluation Kinds oflinking solutions dry adhesive Concentrations Viscosities AppearanceLight resins agents (%) layers (nm) Kinds (%) (cP) faults leakageDurability Example 1 AA modified Methylol 0.50 31 Pure — 1 ∘ ∘ ∘ PVAmelamine water Example 2 AA modified Methylol 0.75 67 Pure — 1 ∘ ∘ ∘ PVAmelamine water Example 3 AA modified Methylol 1.00 124 Pure — 1 ∘ ∘ ∘∘PVA melamine water Example 4 AA modified Methylol 2.00 212 Pure — 1 ∘ ∘∘∘ PVA melamine water Example 5 AA modified Glyoxal 0.50 34 Pure — 1 ∘ ∘▴ PVA water Example 6 AA modified Glyoxal 0.75 64 Pure — 1 ∘ ∘ ▴ PVAwater Example 7 AA modified Glyoxal 1.00 118 Pure — 1 ∘ ∘ ▴ PVA waterExample 8 AA modified Glyoxal 2.00 209 Pure — 1 ∘ ∘ ▴ PVA water Example9 AA modified Glutar- 0.50 32 Pure — 1 ∘ ∘ ▴ PVA aldehyde water Example10 AA modified Glutar- 0.75 65 Pure — 1 ∘ ∘ ▴ PVA aldehyde water Example11 AA modified Glutar- 1.00 122 Pure — 1 ∘ ∘ ▴ PVA aldehyde waterExample 12 AA modified Glutar- 2.00 205 Pure — 1 ∘ ∘ ▴ PVA aldehydewater Example 13 PVA Methylol 0.50 30 Pure — 1 ▴ ∘ ▴ melamine waterExample 14 PVA Methylol 0.75 63 Pure — 1 ▴ ∘ ▴ melamine water Example 15PVA Methylol 1.00 127 Pure — 1 ▴ ∘ ▴ melamine water Example 16 PVAMethylol 2.00 211 Pure — 1 ▴ ∘ ▴ melamine water Example 17 AA modifiedMethylol 0.50 31 Aqueous Methylol 3 ∘ ∘ ∘ PVA melamine solution melamine(5%) Example 18 AA modified None 0.50 31 Aqueous Methylol 3 ∘ ∘ ∘∘ PVAsolution melamine (5%) Example 19 AA modified None 1.00 125 AqueousMethylol 3 ∘ ∘ ∘∘ PVA solution melamine (5%) Example 20 AA modified None1.00 150 Aqueous Methylol 4 ∘ ∘ ∘∘ PVA solution melamine (10%) Example21 AA modified None 1.00 127 Pure — 1 ∘ ∘ ▴ PVA water Example 22 AAmodified None 1.00 127 Aqueous Methylol 4 ∘ ∘ ∘ PVA solution melamine(5%) Example 23 AA modified None 1.00 128 Aqueous Methylol 5 ∘ ∘ ∘ PVAsolution melamine (10%) Example 24 AA modified None 1.00 127 AqueousMethylol 6 ∘ ∘ ∘ PVA solution melamine (20%) Example 25 AA modifiedMethylol 1.00 119 Pure — 1 ∘ ∘ ∘ PVA melamine water Example 26 AAmodified Methylol 1.00 119 Aqueous Methylol 4 ∘ ∘ ∘ PVA melaminesolution melamine (5%) Example 27 AA modified Methylol 1.00 120 AqueousMethylol 5 ∘ ∘ ∘ PVA melamine solution melamine (10%) Example 28 AAmodified Methylol 1.00 120 Aqueous Methylol 6 ∘ ∘ ∘ PVA melaminesolution melamine (20%) Example 29 AA modified Methylol 1.00 122 Pure —1 ∘ ∘ ∘ PVA melamine water Example 30 AA modified Methylol 1.00 124 Pure— 1 ∘ ∘ ▴ PVA melamine water Example 31 AA modified Methylol 1.00 120Pure — 1 ∘ ∘ ▴ PVA melamine water Example 32 AA modified Methylol 1.00118 Pure — 1 ∘ ∘ ∘∘ PVA melamine water Comparative AA modified Methylol0.50 16 None — — x ∘ x Example 1 PVA melamine Comparative AA modifiedMethylol 0.75 20 None — — x ∘ x Example 2 PVA melamine Comparative AAmodified Methylol 1.00 23 None — — x ∘ x Example 3 PVA melamineComparative AA modified Methylol 2.00 27 None — — x ∘ ▴ Example 4 PVAmelamine Comparative AA modified Methylol 2.50 32 None — — x ∘ ∘ Example5 PVA melamine Comparative AA modified Methylol 3.00 52 None — — x ∘ ∘Example 6 PVA melamine Comparative AA modified Methylol 3.50 83 None — —x ∘ ∘ Example 7 PVA melamine Comparative AA modified Methylol 4.00 203None — — x ∘ ∘∘ Example 8 PVA melamine Comparative AA modified Glyoxal2.50 34 None — — x ∘ x Example 9 PVA Comparative AA modified Glyoxal3.00 52 None — — x ∘ x Example 10 PVA Comparative AA modified Glyoxal3.50 84 None — — x ∘ x Example 11 PVA Comparative AA modified Glyoxal4.00 195 None — — x ∘ x Example 12 PVA Comparative AA modified Glutar-2.50 32 None — — x ∘ x Example 13 PVA aldehyde Comparative AA modifiedGlutar- 3.00 54 None — — x ∘ x Example 14 PVA aldehyde Comparative AAmodified Glutar- 3.50 87 None — — x ∘ x Example 15 PVA aldehydeComparative AA modified Glutar- 4.00 205 None — — x ∘ x Example 16 PVAaldehyde Comparative PVA Methylol 2.50 33 None — — x ∘ x Example 17melamine Comparative PVA Methylol 3.00 51 None — — x ∘ x Example 18melamine Comparative PVA Methylol 3.50 86 None — — x ∘ x Example 19melamine Comparative PVA Methylol 4.00 203 None — — x ∘ x Example 20melamine Comparative AA modified Methylol 1.00 21 None — — x x x Example21 PVA melamine

In Table 1, PVA means polyvinyl alcohol, and AA modified PVA means apolyvinyl alcohol-based resin containing an acetoacetyl group.

A polarizing plate obtained by means of a manufacturing method of theinvention is preferably employed alone as it is or as an optical filmmanufactured by laminating the polarizing plates in a liquid crystaldisplay, a flat panel display such as an electroluminescence display oran image viewing display such as a plasma display panel (PDP).

1. A method for manufacturing a polarizing plate in which a transparent protective film is provided on at least one surface of a polarizer with an adhesive layer interposed therebetween, wherein an adhesive is coated on a surface of the transparent protective film on which the adhesive layer is formed or/and a surface of the polarizer on which the adhesive layer is formed to form the adhesive layers, and thereafter, an aqueous liquid, which comprises no adhesives, is caused to be present on an adhering surface when the transparent protective film and the polarizer are continuously adhered to each other with the adhesive layer interposed therebetween.
 2. The method for manufacturing the polarizing plate according to claim 1, wherein the polarizer is a polyvinyl alcohol-based polarizer and the transparent protective film is a cellulose-based transparent protective film.
 3. The method for manufacturing the polarizing plate according to claim 1, wherein a thickness of the polarizer is 35 μm or less.
 4. The method for manufacturing the polarizing plate according to claim 1, wherein the adhesive is a polyvinyl alcohol-based adhesive.
 5. The method for manufacturing the polarizing plate according to claim 4, wherein the polyvinyl alcohol-based adhesive is a polyvinyl alcohol-based adhesive having an acetoacetyl group.
 6. The method for manufacturing the polarizing plate according to claim 1, wherein the adhesive comprises a crosslinking agent.
 7. The method for manufacturing the polarizing plate according to claim 6, wherein the crosslinking agent is a methylol compound.
 8. The method for manufacturing the polarizing plate according to claim 1, wherein a thickness of the adhesive layer is in the range of 30 to 300 nm.
 9. The method for manufacturing the polarizing plate according to claim 1, wherein a viscosity of the aqueous liquid is in the range of 0.1 to 10 cP.
 10. The method for manufacturing the polarizing plate according to claim 6, wherein the aqueous liquid is water.
 11. The method for manufacturing the polarizing plate according to claim 1, wherein the aqueous liquid is an aqueous solution comprising a crosslinking agent dissolved therein.
 12. The method for manufacturing the polarizing plate according to claim 11, wherein the crosslinking agent is a methylol compound.
 13. The method for manufacturing the polarizing plate according to claim 1, wherein the aqueous liquid is supplied on an adhering surface between the transparent protective film and the polarizer.
 14. The method for manufacturing the polarizing plate according to claim 1, wherein the adhesive is coated only onto the transparent protective film side and the aqueous liquid is supplied on the adhesive layer formed by the coating to thereby cause the aqueous liquid to be present on the adhering surface.
 15. The method for manufacturing the polarizing plate according to claim 1, wherein the adhesive is coated only onto the transparent protective film side, while the aqueous liquid is supplied onto the polarizer side to thereby cause the aqueous liquid to be present on the adhering surface.
 16. The method for manufacturing the polarizing plate according to claim 1, wherein the adhesive is coated only onto the polarizer side, while the aqueous liquid is supplied onto the transparent protective film side to thereby cause the aqueous liquid to be present on the adhering surface.
 17. The method for manufacturing the polarizing plate according to claim 1, wherein the aqueous liquid is supplied onto an adhering surface just before adhesion when the transparent protective film and the polarizer are continuously adhered to each other with the adhesive layer interposed therebetween.
 18. A polarizing plate obtained by the method according to any one claim
 1. 19. An optical film comprising at least one polarizing plate according to claim
 18. 20. An image viewing display comprising the polarizing plate according to claim
 18. 